Epoxy resin-biphenyl anhydride adhesive compositions



United States Patent US. Cl. 26037 15 Claims ABSTRACT OF THE DISCLOSUREA new epoxy resin adhesive composition having high initial tensile lapshear strength which is retained on heat aging is claimed as is themethod of preparation. The composition contains an epoxy resin, certainsolid biphenyl anhydrides having at least one anhydride function on eachphenyl group, and a powdered metal. The composition is prepared bysuspending the solid biphenyl anhydride in the epoxy resin by a highshear mixing force.

This invention relates to new and useful epoxy resin adhesivecompositions which on curing have excellent retention of tensile lapshear strength values after heat aging.

This application is a continuation-in-part of our prior co-pendingapplication, Ser. No. 334,716, filed Dec. 31, 1963, now US. Patent3,324,081.

Epoxy resins are well known in the art and comprise a molecule whichcontains on the average more than one epoxy group. The resins areconverted into hard, infusible cross-linked polymers by curing. Curingof the resins may be effected by a catalytic type polymerization processor by a coupling type process. The compositions of the subject inventionare formed by the coupling type process wherein the epoxy resin isreacted with polyfunctional cross-linking agents to be defined to coupleor cross-link one epoxy resin molecule with another.

The properties of the epoxy resins and the cured reaction products willdepend, of course, on the nature of the epoxy resins and thecross-linking agents. It is desirable for some adhesive applicationsthat the adhesive have a high initial tensile lap shear strength andretain high tensile lap shear strength even after being subjected toelevated temperatures for extended periods of time. For example, in theadhesion of metal parts for use in high temperature work, it isfrequently important that the adhesive bonds not fail over extendedperiods of time. It is also desirable to be able to apply these adhesivecompositions at room temperature so that no elaborate and expensiveapplication techniques are required.

It has been found that all of the above desirable results are achievedby the epoxy resin adhesive compositions of this invention.

In accordance with the invention a new adhesive composition suitable forapplication at room temperature and which on curing results in a resinhaving excellent tensile lap shear strength retention properties afterheat aging comprises:

A suspension ofice A solid biphenyl anhydride selected from the groupconsisting of:

where x and y are monovalent radicals selected from the group consistingof H; an alkyl group having between 1 ailld 5 carbon atoms; a halogen;OH; OR, where R is an alkyl group having between 1 and 5 carbon atoms;and

where R is as defined; and where R and R are monovalent radicalsselected from the group consisting of H; an alkyl group having between 1and 5 carbon atoms; and a halogen; and a finely divided solid fillercomprising a powdered metal in a liquid 1,2-epoxy resin which contains0n the average more than one 1,2-epoxy group per molecule; the amount ofsaid powdered metal being at least 20 parts per parts of resin and theamount of said solid biphenyl anhydride being such that the anhydride toepoxide equivalent ratio is between 0.4 and 1.0.

Any of the liquid epoxy resins well known in the art can be employed inthe new compositions of this invention. By an epoxy resin is meant anymolecule which contains on the average more than one epoxy group. Anepoxy group is a three-membered ring containing one oxygen and twocarbon atoms. The liquid aromatic type epoxy resins are preferred. Themore preferred epoxy resins are generally prepared by the reaction of anepihalohydrin with (1) a polyhydric alcohol, (2) a phenol.

or (3) a phenol-formaldehyde product. The reaction products are complexmixtures of polyethers having terminal 1,2-epoxide groups and in whichalternating intermediate aliphatic hydroxy-containing radicals arelinked through ether oxygens to aliphatic or aromatic nuclei. Othersuitable epoxy resins include, for example, butane dioxide and limonenedioxide.

The high molecular weight complex polyether compositions arethermoplastic, but are capable of forming thermosetting compositions byfurther reaction through the hydroxy and/or 1,2-epoxide groups with across-linking agent. In order to form these thermosetting compositions,the epoxy resin must have a 1,2-epoxide equivalency greater than one. Byepoxide equivalency is meant the average number of 1,2-epoxide groupscontained in the measured molecular weight of the resin. Since the epoxyresin is a mixture of polyethers, the measured molecular weight, uponwhich the 1,2-epoxide equivalency depends, is necessarily an averagemolecular weight. Hence, the 1,2

epoxideequivalency of the resin will be a number greaterthan one, butnot necessarily an integer. L? the measured molecular weight and epoxidevalue are given, the 1,2- epoxide equivaiency can easily be determined.For example,-an epoxy resin having an average molecular weight of 900and an epoxide value of 0.2 has a 1,2-epoxide equivalency of 1.8. V a

The epoxide value of an epoxy resin is the number of epoxide groups per100 grams of resin. This value can be determined experimentally byheating a one gram sample of the epoxy resin with an excess of apyridine solution of pyridine hydrochloride (obtained by adding sixteencc. of concentrated hydrochloric acid to a liter of pyridine) at theboiling point for twenty minutes and then back titrating the unreactedpyridine hydrochloride with 0.1 N NaOH to the phenolphthalein end point.In the calculations, each HCl consumed by the resin is considered to beequivalent to one epoxide group.

g The preferred epoxy resins are prepared by the reaction ofepichlorohydrin with a dihydric phenol and have 20 the general formula:

When n in the above formula is zero, a diglycidyl ether having thefollowing formula results:

The above ether can be obtained when the mol ratio of epichlorohydrin tobisphenol A isabout 1. Lower ratios will produce higher moiecular weightpolyethers. .For the preferred resins which have a molecular weightbetween about 350 and 600, the mol ratio of epichlorohydrin to.

bisphenol A can be between about 1:1 and 10:1. Refer ring to the generalformula above, for the preferred resins, n will Vary'betWeenO' and 1.The epoxide equivalent (which is defined as the weight of resin in gramscontaining 1 gram equivalent of epoxy) should be between about 175 and300, which is one-half the average molecular weight. The viscosity ofthe polyther will vary from 3,000 to 30,000 cps at Q. Many commerciallyavailable epoxy resins with suitable properties may be employed. Forexample, suitable resins include Bakelite BEL-2774; Bakelite ERL-3794;Epi-Rez 510; Epon 820 and Epon 828. Bakelite is the trademark of UnionCarbide Corporation; Epi-Rez is the trademark of Jones-Dabney Co.,Division oi Devoe and Reynolds Co.; and Epon is the trademark of theShell Chemical Co. e

The epoxy resins used in the compositions of this invention are hardenedor'cured by the use of at least one anhydride cross-linking agent. Theone anhydride is a biphenyl anhydride having at least one anhydridefunction on each phenyl group and wherein the phenyl groups are linkedthrough a single carbon atom.

The preferred biphenyl dianhydrides are selected from the groupconsisting of;

and V a where x and y are monovalent radicals selected from the groupconsisting of H; an alkyl group having between 1 and 5 carbon atoms; ahalogen; OH; OR, whereR is an alkyl group having between 1 and '5 carbonatoms; and

where R is an alkyl group having between 1 and 5 carbon atoms; and whereR and R are monovalent radicals selected from the group consisting of H;an alkyl group having between 1 and 5 carbon atoms; and a halogen;

Suitable examples of biphenyl anhydrides which can be utilized in thecompositions of this invention are given oelow:

3,4,3',4'-diphenylrnethane tetracarboxylic dianhydride;2,3,2,3'-diphenylmethane tetracarboxylic dianhydride; 2,3,3,4'-diphenylmethane' tetracarboxylic dianhydride; 2-methy'l-3,4,3',4-diphenylmethane tetracarboxylic dianhydride; 2,2'-dimethyl-3,4,3',4-diphenylmethane tetracarboxylic dianhydride;2-ethyl-2'-propyl-3,4,3,4'-diphenylmethane tetracarboxylic dianhydride;2-amyl3,4,3',4'-diphenylmethane tetracarboxylic' dianhydride;

2-butyl-2'-propyl-3,4,3',4-diphenyl-methane tetracarboxylic dianhydride;

chloro-3,4,3',4-diphenylmethane tetracarboxylic dianhydride;

dichloro-3,4,3',4'-diphenylmethane tetracarboxylic dianhydride;

bromo-3,4,3,4-diphenylmethane tetracarboxylic dianhydride;

dibromo-3,4,3',4'-diphenylmethane tetracarboxylic dianhydride;

3,4,3',4-benzhydrol tetracarboxylic dianhydride;

2,3,2',3'-benzhydrol tetracarboxylic dianhydride;

2,3,3,4'-benzhydrol tetracarboxylic dianhydride;

2-methyl-3,4,3',4-benzhydrol tetracarboxylic dianhydride;

2,2-dimethyl-3,4,3',4'-benzhydrol tetracarboxylic dianhydride;

2-butyl-2-propyl-3,4,3',4'-benzhydrol tetracarboxylic dianhydride;

3,4,3',4'-benzhydrol tetracarboxylic dianhydride methyl ether;

3,4,3,4-benzhydrol tetracarboxylic dianhydride ethyl ether;

2,3,3',4-benzhydrol tetracarboxylic dianhydride propyl ether;

2,3,2',3'-benzhydrol tetracarboxylic dianhydride butyl ether;

3,4,3',4'-benzhydrol tetracarboxylic dianhydride acetate;

3,4,3,4-benzhydrol tetnacarboxylic dianhydride propionate;

2,3,3',4-benzhydrol tetracarboxylic dianhydride butyrate;

3,4,3',4-benzophe11one tetracarboxylic dianhydride;

2,3,2',3-benzophenone tetracarboxylic dianhydride;

2,3,3',4'-benzophenone tetracarboxylic dianhydride;

2-methyl-3,4,3',4-benzophenone tetracarboxylic dianhydride;

2,2"-dimethyl-3,4,3',4-benzophenone tetracarboxylic dianhydride;

2-ethyl-2-methyl-3,4,3',4'-benzophenone tetracarboxylic dianhydride;

2-butyl-2'-ethyl-3,4,3',4'-benzophenone tetracarboxylic dianhydride;

2-amyl-3,4,3',4'-benzophenone tetracarboxylic dianhydride;

2-butyl-2-propyl-3,4,3',4-benzophenone tetracarboxylic dianhydride2-chloro-2'-methyl-3,4,3,4'-benzophenone tetracarboxylic dianhydride;

It has also been found that the activity of the biphenyl anhydride is afunction of the free acid content of the anhydride. It is preferred thatthe phenyl anhydride be substantially free of carboxylic acid groups,and in. any case, the percent free acids in the biphenyl anhydrideshould be less than 6 weight percent, and preferably less than about 2weight percent.

The ratio of the chemical anhydride equivalents of the biphenylanhydrides to the chemical epoxide equivalents of the epoxy resin (anA/E ratio) is suitably maintained between 0.4 and 1.0 with a preferredratio between 0.55 and 0.9 and a most preferred ratio between 0.58 and0.63.

It has been found that the addition of fillers comprising a powderedmetal and, in particular, the addition of a combination of a metallicand non-metallic oxide filler results in adhesive formulations havingunexpectedly high initial tensile lap shear strengths which strengthsare retained over extended periods of heat aging. Suitable metallicfillers include finely divided (powdered) metals, exemplified but notlimited to aluminum and iron.

Non-metallic fillers alone appear to decrease the tensile lap shearstrength of the adhesives of this invention. On the other hand, theaddition of a non-metallic oxide, such as silicon dioxide, along withthe powdered metal has an unexpected effect on increasing the tensilelap shear strength of the adhesive. The non-metallic oxide should befinely divided, of course. In addition to the silicon dioxide mentionedabove, suitable non-metallic oxide materials include alumina, calciumcarbonate, magnesium silicate, alumina silicate, kaolin, hydratedalumina and thixotropic agents, such as bentonite clays.

The fillers both metallic and non-metallic oxide can range in particlesize between 200 mesh to about 0.015 micron. The amount of filler to beemployed depends to some extent upon the thickening properties of theparticular filler chosen. The metallic fillers, such as powderedaluminum, tend to have less thickening effect on the epoxy resin thanthe non-metallic materials, such as the alumina silicates. The amount ofmetallic filler should be at least 20 parts per hundred parts of resin(phr.) and can suitably be as high as 200 partstper hundred parts ofresin (phr.) with the preferred amount of metallic filler being betweenand phr. Much lower amounts of the non-metallic oxide thickener typefillers are employed, amounts between 1 and 50 parts being generallysatisfactory and preferred amounts being between 1 and 20 phr.

As noted, the best adhesive formulations are those which use acombination of a powdered metallic filler, such as aluminum, and afinely divided non-metallic oxide filler, such as silicon dioxide.Particularly preferred combinations are those using between 80 and 120*phr. of powdered metals and between 1 and 10 phr. of the non-metallicoxide fillers.

It has been found that the biphenyl anhydride crosslinking agentsdefined above are substantially insoluble in the liquid epoxy resins atroom temperature. The solubility of the biphenyl anhydrides in theliquid epoxy resins increases upon heating the liquid epoxy resin, butdue to the high functionality and therefore the high activity of thebiphenyl anhydrides, the heating of the epoxy resin before or during theaddition of the biphenyl crosslinking agent results in rapid gelationand solidification of the epoxy resin composition. What is desired is toincorporate the biphenyl anhydride cross-linking agent into the epoxyresin at a low temperature, such as room temperature, so that theadhesive composition can be applied at room temperature and yet possessand retain high tensile lap shear strength values upon curing at anelevated temperature. Suggestions have been made to employ a commonsolvent to prepare solutions of reactive cross-linking agents in epoxyresins; however, the biphenyl anhydride cross-linking agents definedabove are substantially insoluble in most materials. A method has nowbeen found for preparing the epoxy resin adhesive compositions definedabove at a low temperature between about 20 and about 40 C. andpreferably at room temperature wherein the composition is stable, can beapplied at room temperature and cured at elevated temperatures to giveadhesive bonds which have high initial tensile lap shear strengths andwhich high shear strengths are retained over long periods of time underelevated temperatures. This method consists of suspending the finelydivided solid biphenyl anhydride in the liquid epoxy resin. Thesuspension is formed by subjecting a mixture of the powdered solidbiphenyl anhydride and the liquid epoxy resin to a high shear mixingaction for a time sufiicient to maintain the solid biphenyl anhydride insuspension at room temperature for a period of at least seven days. Anysuitable means can be employed to achieve the desired suspension. Onesuitable means involves passing the admixture of the finely dividedsolid biphenyl anhydride and the liquid epoxy resin through a three-rollmill. Other suitable means would include the use of ball mills or chainmills. Simple mechanical stirring has been found to be insufficient toachieve the desired results, especially with the lower viscosity liquidepoxy resins.

After the incorporation of the solid biphenyl anhydride into the liquidepoxy resin to form a suspension, the desired fillers in the abovedescribed amounts can then be added with simple mechanical stirring ifthe powdered metals are sufliciently finely divided.

Properties of the hardened epoxy resins are affected by the curingconditions wherein more complete crosslinking occurs. Curing can occurat temperatures between about 150 and 280 C. for time periods as shortas five minutes to times as long as two days or more. In general, thehigher the curing temperature, the shorter the time required to producea completely cured epoxy resin product. The preferred curingtemperatures are between 150 and 240 C. at cure times between 0.5 and 48hours with more preferred cure times between 1 and 5 hours.

The adhesive compositions of this invention are applied to a suitablesubstrate at room temperature or thereabouts before curing. Sinceelevated temperatures are required for curing, the substrate should besuch that it is not damaged by the high curing temperatures required.Normally, the adhesives of this invention are employed for theattachment of one metallic part to another, although ceramic or otherheat resistant materials can also suitably be joined together with theadhesive compositions of this invention. It has been found that theprior treatment of the substrate is important so far as the strength ofthe tensile lap shear bond obtainable is concerned. For example, themetallic surface can be sandblasted or acid-etched, with acid-etchingbeing the preferred procedure for preparing a metal surface for bondingusing the adhesive compositions of this invention.

In addition, various well-known cu-re accelerators, such as tertiaryamines, can be added to the compositions, if desired. Suitableaccelerators include benzyl-dirnethylamine;alpha-methylbenzyldimethylamine; dimethylaminopropylamine;dimethylaminomethyl phenol (DMP- by Rohm and Haas); and tris(dimethylaminomethyl) phenol (DMP-30). Strongly acidic materials, suchas boron trifluoride, can also be used.

The invention will be further described with reference to the followingexperimental work.

Unless otherwise indicated, the epoxy resin employed in the series ofepoxy resin compositions to be discussed below was Epon 828, acommercial liquid aromatic type epoxy resin sold by Shell ChemicalCompany. Epon 828 has an epoxide equivalent of 175-210 and a viscosity(cps.) at 25 C. between 10,000 and 20,000. The epoxide equivalent isdefined as the weight of epoxy resin Containing one equivalent weight ofepoxide. Epon 828 is characterized as the reaction product of bisphenolA and epichlorohydrin.

The biphenyl anhydride used in all of the adhesive compositions was3,3',4,4-benzophenone tetracarboxylic dianhydride (hereinafter BTDA).The BTDA was ground to a fine powder form (will pass through a 325 meshscreen) and was added to the Epon 828 at room temperature. The mixtureof Epon 828 and BTDA was then subjected to high shear mixing in athree-roll mill (purchased from Charles Ross and Son Co., Inc. ofBrooklyn, N.Y.) for a time sufiicient to result in a stable suspensionof the BTDA in the Epon 828. By a stable suspension is meant the BTDAdid not noticeably settle out on standing for a period in excess ofseven days at room temperature.

Usually between 2 and 10 runs through the mill are sufficient whichtakes between 1 and 10 minutes of mixing.

A first series of epoxy resin compositions was prepared using Epon 828as the epoxy resin and BTDA as the crosslinking agent at varying A/Eratios. The BTDA was added using a three-roll mill as noted above.Fillers consisting of aluminum powder and Cab-O-Sil were next added withmechanical stirring at room temperature. No accelerator was employed.The composition was used to join two 4- x 1 x 0.0625 inch pieces ofsandblasted Alclad aluminum in accordance with the test procedure ofASTM D1002 for tensile lap shear strength. The Alclad aluminum pieceswere joined together over a one square inch area with the adhesivecomposition wherein the adhesive composition had a thickness between 1-5mils. The joined pieces were cured at 200 C. for two hours. The tensilelap shear values at varying temperatures using varying A/E ratios isshown in Table I below. In the data in Table I below and the other datato be presented, the tensile lap shear strength test was run at theactual temperatures stated, i.e. 73 F., 300 F. or 500 F. The specimenswere heated to the temperature indicated in an oven and held there forabout 10 minutes before the test was performed while the specimensremained in the oven.

TABLE I.BTDAEPON 828 ADHESIVES PERATURE HIGH TEM [Variation of A/ERatio] phr. atomized aluminum powder 3 phr. Oab-O-Sil 1 1 Cab -O-S1l 1stradename of Cabot corporation for silicon dioxide which is asubmicroscopic pyrogenic silica prepared in a hot gaseous environment(1,100 C.) and which has an external surface area of 200 sq uiiielmgters1t erdgram anfd a partlicle size of 0.015 micron.

c a is a la ename or an a uminum allo containin 3.8 to 4.9 copper soldby Alcoa as Alclad 2024T3. y g

@ ASTM Test N o. D1002-531.

Referring to Table I, it can be seen there is little differ ence betweenthe values for tensile lap shear at the varying A/E ratios tried. Sincethe biphenyl anhydride is usually the more expensive component, thelowest A/ E ratio consonant with obtaining the desired results ispreferred. An A/ E ratio of about 0.6 is therefore the preferred ratio.

A second series of epoxy resin compositions having an A/E ratio of 0.6was prepared using varying amounts and types of fillers. The results ofthese runs are shown on Table II below.

TABLE II.USE OF FILLERS TO IMPROVE TENSILE LAP SHEAR STRENGTH INBTDA-EPON 828 ADHESIVE FOR- MULATIONS [Acid Etched Alclad AluminumFillers, phr. Tensile 9 Aluminum shear, A/E powder Cab-O-Sil p.s.i.

Example N 0.

1 Aluminum was cleaned with trichloroethylene to degrease and thenetched by stirring the aluminum at F. for 5-10 minutes in a solution of10% sodium dlchromate; 20% sulfuric acid (96% H2804 by weight); and 70%water.

Referring to Table II, Example 5 shows that when no filler is employed,a tensile lap shear strength of 1770 9 10 p.s.i. is obtained. Example 6shows the addition of 100 trolled within several percent of the desiredtemperature phr. of powdered aluminum increases the tensile lap shearand, after remaining at the desired temperature (500 F.)

strength to 2080 p.s.i. while the addition of 3 phr. of for a prescribedlength of time, the specimens were tested Cab-O-Srl has no elfect(Example 7). Example 8 shows by ASTM test D1002 at 500 F. to determinethe tensile the more than additive efiFect of adding both the powderedlap shear strength. The results of the tests are shown in aluminum (100phr.) and the thickening agent Cab-O-Sil Table V below.

TABLE V.-PERCENT RETENTION OF TENSILE LAP SHEAR STRENGTH AFTER HEATAGING AT 482 F (250 C.) OF BTDA-EPOXY AND EPOXYLITE HIGH TEMPE RATUALUMINUM SUBSTRATES RE ADHESIVES ACID ETCHED ALOLAD Tensile Lap Shear,p.s.i. at 500 F.

Composition of Example N o 15 10 11 12 13 14 D011 y D011 esi e BTDA,Epon DEN 43s: DEN 438:

828, A/E=0.6 A/E=0.6 A/E=0.6 5403 5523 5524 TLS 1 at 500 F. (5-10minutes at 500 F.) 1, 220 700 TLS 2 after 500 hrs. aging at 500 F 1, 0901 020 1 858 gig Percent retention 90 140 1e0 e4 37 After 1,000 hrs.aging at 500 1, 040 110 150 Percent retention 85 15 9.6

1 Tensile lap shear strength actually run at 500 F. 2 Tensile lap shearactually run at 500 F. 3 Fell apart. (3 phr.) 1n achieving a tensile lapshear strength of 2480 Referring to Table V, Example 15 shows a 90percent P- retention after 500 hours at 500 F. while the Epoxylite Athird series of epoxy resin compositions having an o A/ E ratio of 0.6was prepared using 100 phr. of powdered ig f pig i i jgg g 3 232215 22:

1 alummum and 3 Phr of Cab 0 S11 as the fil ers In thls invention had an85 percent retentlon of tensile lap shear series, a ortion of the epoxresin was su lied b Dow o Chemical! company,s Nogolac resin gg z asstrength at 500 F. while the remamlng commerclal ad- DEN The results areShown in Table III below hesives decreased to 15 and 9.6 percentretention.

TABLE IIL-BTDA-EPON szaoow DEN 43s NOVOLAC ADHESIVES, HIGH TEMPERATURE[Variation of Epon 828/Novolac Ratio] 100 phr. aluminum 3 phr. Cab-O-SilNo accelerator sandblasted Alclad Al 2 hr. cure at 200 C.

Tensile Lari: Shear, p.s.i. a

Test Temp., F.

Referring to Table III, Example 9 is the same as Ex- 45 Again referringto Table V Examples 15, 10 and 11 ample The mclusfon of other types ofepoxy show that after 500 hours, the tensile lap shear strength(ExampleslO-ll) grves about the same results showing values for the Epon828 and mixed epoxies were about that mlxtures of epoxy resms can beemployed the same (1090, 1020 and 1080 respectively). Note the TheBTDA-Epon 828 adhesive compositions were cominitial tensile lap shearstrength for the Epon 828 alone pared 'with commercially avallableEpoxyllte high tern p was 1220 p s s o ly 700 and 675 rature adhesivesfrom the Epoxylite Corporation. The :sults are Shown in Table IV belowfor the mixed epoxies (Examples 10 and 11). The pre- TABLE IV.EVALUATIONOF EPOXYLITE HIGH TEMPERATURE ADHESIVES [Comparison With BTDA Adhesives]Tensile Lap Shear, p.s.i. at-

73 F. 300 F. 500 FJ 1 Contains 100 phr. of powdered aluminum and 3 phr.of Cab-O-Sil. Z Epoxylite-Tradename oi Epoxylite Corporation.

3 Actually run at 300 F.

4 Actually run at 500 F.

Referring to Table IV, the Epoxylite adhesives all had ferred epoxyresin is therefore the type represented by poorer strengths at 73 F. butEpoxylite 5524 possessed E9011 slflfie hlgll lnitial tensile P ShearStrengths good high temperature tensile lap shear strength pro areobtained in addition to good heat aging charactererti istics. The lowerinitial values for tensile lap shear The compositions of Examples 10-15above were then strengths in Examples 10 and 11 are believed due toinsubjected to a heat aging test at 250 C. (482 F.) to suflicient curingat the time the test was run.

determine the elfect of heat on the tensile lap shear values A finalseries of epoxy resin compositions was preof these adhesives afterextended periods of time, The pared using various fillers and tested fortheir tensile lap heat aging test was run by placing the specimens intoa shear values at 73 F. The results of this series is shown hightemperature oven wherein the temperature is conbelow in Table VI.

TABLE VL-EFFECT F FILLERS ON TENSILE LAP SHEAR V: STREN QTH 0F BTDAADHESIVES AT 73 F.

BTDA-Epon 828 at A[E=0.6 Cure: 2 hours, 200 C: r

'Alclad Aliiminim Substrate (Acid Etched) f Example r I Tensile LapShear, at

Fillers tion at room temperature and which on curing results in a resinhaving excellent tensile lap shear strength retention properties afterheat aging which consists of:

Referring to Table VI, only the aluminum and iron (Examples 17, 18 and19) increased the tensile lap shear strength oventhe base run (Example16). Examples 20- employed non-metallic fillers and all decreased thetensile lap shear strength of the adhesive.

Resort may be had to su h varlatlons and modificathe anhydride toepoxide equivalent ratio is between 0.4 and 1:0

2. A composition according to claim 1 wherein said solid biphenylanhydride is benzophenone tetracarboxylic acid dianhydride.

3. A composition according to claim 1 wherein the A/E ratio is between0.55 and 0.9. 5

4. A composition according to claim 1 wherein said powdered metal isiron.

5. A composition according to claim 1 wherein said powdered metal isaluminum.

6. A composition according to claim 1 wherein said filler comprises apowdered metal in amounts between 20 and 200 phr. and a finely dividednon-metallic oxide in amounts between 1 and phr.

7. A composition according to claim 6 wherein the powdered metal isaluminum and the non-metallic oxide is silicon dioxide.

8. A composition according to claim 6 wherein the solid biphen'ylanhydride is benzophenone tetracarboxylic acid dianhydride and the epoxyresin has the general formula:

tions as fall within the spirit of the invention and the scope of theappended claims. a

We claim: 1. A new adhesive composition suitable for applicaa suspensionof a solid biphenyl anhydride selected from the group consisting of:

where x and y are monovalent radicals selected from the group consistingof H; an alkyl group having between 1 and :5 carbon atoms; ahalogen;.OH; OR;;where R is an alkyl group having between 1 and 5 carbonatoms; and i ii -OC;R

where R is as defined; and where R and R are monovalent radicalsselected from the group consisting of H; an'alkyl group having between 1and 5 carbon atoms; and a halogen;

where R is a divaient aromatic radical and n is an integer between 0 andabout 18, and the A/E ratio is between 0.58 and 0.63.

9. A composition according to claim 8 wherein the epoxy resin containsin addition at least a portion of the reaction product of (1)epichlorohydrin with (2) the reaction product of phenol andformaldehyde.

10. A method of producing an adhesive composition suitable forapplication at room temperature and which on curing results in a resinhaving exceilent tensile lap shear strength retention properties afterheat aging which comprises:

suspending a finely divided solid biphenyl anhydride selected from thegroup consisting of:

wherex and y are monovalent radicalsiselected from the group consistingof H; an alkyl group having between 1 and 5 carbon atoms; a halogen; OH;OR, where R is an alkyl group having between 1 and 5 carbon atoms; and

O 7V -o- ('1-R .where R is as defined; and gwhere R and R are monovalentradicals selected from the group consisting of H; an alkyl group havingbetween 1 and 5 carbon atoms; and a halogen; in liquid 1,2-epoxy resinwhich contains on the average more than one 1,2-epoxy groups permolecule, the amount or" said solid biphenyl anhydride being such thatthe A/E equivalent ratio is between 0.4 and 1.0;

13 said suspension being formed at a temperature between about 20 andabout 40 C. by subjecting an admixture of said solid biphenyl anhydrideand said liquid epoxy resin to a high shear mixing action sufiicient tomaintain the 14 comprises a finely powdered aluminum in an amountbetween 80 and 120 phr. and a finely divided non-metallic oxide in anamount between 1 and 10 phr.; the solid biphenyl anhydride isbenzophenone tetracarboxylic acid dianhydride and the epoxy resin hasthe general formula:

solid biphenyl anhydride in suspension at room and adding to saidsuspension by stirring a filler comprising a powdered metal in an amountof at least 20 phr.

11. A method according to claim 10 wherein the suspension is formed atsubstantially room temperature.

12. A method according to claim 11 wherein the suspension is formedusing a three-roll mill.

13. A method according to claim 10 wherein said biphenyl anhydride isbenzophenone tetracarboxylic dianhydride.

14. A method according to claim 10 wherein the filler comprises a finelypowdered metal in an amount between 20 and 200 phr. and a finely dividednon-metallic oxide in an amount between 1 and 50 phr.

15. A method according to claim 11 wherein the filler where R is adivalent aromatic radical and n is an integer temperature for a periodof at least seven days; 10 between 0 and about 18.

References Cited UNITED STATES PATENTS 15 3,183,198 5/1965 Wagner.

3,280,043 10/1966 Larson. 3,324,081 6/1967 Barie et al. 3,337,509 8/1967Budnowski. 3,284,398 11/1966 Warren et al. 26037 20 3,344,096 9/1967Manasia et al. 260-37 ALLAN LIEBERMAN, Primary Examiner L. T. JACOBS,Assistant Examiner US. Cl. X.R. 2602, 47, 59

